Viewfinders for use with video cameras, etc., to observe an enlarged image of an image displayed on a display screen with a naked eye are conventionally known. Such a viewfinder uses an eyepiece optical system for observing an enlarged image of a liquid crystal display screen. In recent years, more and more digital cameras use this type of viewfinders (which are also referred to as electronic viewfinder or EVF).
As a triplet eyepiece optical system usable with the above-described electronic viewfinders, eyepiece optical systems disclosed in Japanese Unexamined Patent Publication Nos. 2002-048985, 2007-264179, 2010-175795 and 2010-266776 (hereinafter, Patent Documents 1, 2, 3 and 4, respectively) etc., are proposed.